A reciprocating compressor is a type of positive-displacement compressor, and uses the movement of a piston within a cylinder to move gas from one pressure level to a higher pressure level. Intake gas enters a suction manifold, then flows into a compressor cylinder where it is compressed by a piston driven in a reciprocating motion via a crankshaft. The gas is then discharged via a discharge manifold.
Examples of applications of reciprocating compressors are for oil refineries, gas pipelines, chemical plants, natural gas processing plants and refrigeration plants. For these large compressors, groups of cylinders are operated in parallel.
Conventional reciprocating compressors, especially the large compressors used for natural gas pipelines, have a number of limitations in regard to emissions, efficiency and reliability. These conventional reciprocating compressor fall into two general types: integrated and separable.
“Integrated compressors” are those in which the compressor cylinders and power cylinders are combined in a single integral machine. Both sets of pistons are connected to a single crankshaft via a piston rod. These integral machines run at relatively slow speeds in order to optimize the system efficiency of the combined compressor and power cylinders.
“Separable compressors” are those in which the compressor unit is separated from a power-producing unit, which may be an engine or electric motor. The two units are connected by a set of drive shafts and couplings. The purpose of this configuration is to take advantage of modern emissions control technology for the engine power cylinders. These units run at higher speeds, and the power cylinders run at a little higher efficiency. However, the higher speeds create higher gas velocities in the compressor cylinders, which results in lower compressor cylinder efficiencies.